effect of temperature on beetroot pigment through membrane

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Introduction

Investigating the effect of temperature on the amount of pigment released from a beetroot. Aim: This experiments aims to establish the relationship between temperature and the structure of the cell membrane in a beetroot. When fresh beetroot is left to stand in cold distilled water, very little red pigment is released from the beetroot. When, however, a similar amount of beetroot is places into hot water, pigment release happens more quickly and the surrounding water soon becomes red. An increase in temperature results in an increase of the red pigment release, this could be down to the structure of the beetroot cells' membrane which is a phospholipid bilayer. The temperature affects the H-bonds within the bilayer and the protein pores. Increasing the temperature, increases the kinetic energy within the phospholipid bilayer causing it to break and release pigment into the surrounding water. Independent Variable: Temperature is the variable I am going to change. I will have the temperature at 20oC intervals. The lowest temperature will be just above zero so that the water does not freeze. The maximum temperature will be 80oC high enough to measure an extreme condition but not high enough to let the water boil. The temperatures I will use will be: just above 0oC, 20oC, 40oC, 60oC and 80oC. Dependant Variable: The amount of red pigment in the water will be measured as a light transmission percentage by a colorimeter. Controlled Variables: Beetroot surface area: The surface area of the beetroot disks has to be the same to make it a fair test, all the beetroot disks have to be the same dimensions throughout the experiment. This will be achieved by using a cork borer, standard size 6. The width of the disks is going to be 5mm thick (to 0.5mm degree accuracy) measured by a standard ruler. There will also be the same number of disks per boiling tube, 3 disks, to increase the surface area. ...read more.

Middle

- Record results for each test in the results table. 11. Clean apparatus and repeat the experiment changing the temperature to all specified temperatures - just above 0oC, 20oC, 40oC, 60oC or 80oC - and making sure the same volumes, equipment and method is used. At the end of the experiment there should be 18 light transmission percentage recordings (3 test tubes x 5 temperatures) and 5 average results. Analysis: Graph 1 shows my initial results and their averages for temperatures 10oC, 20oC, 40oC and 60oC. The general trend of the graph looks like a linear negative correlation between temperature and light transmission as a percentage. The results for 10oC (64%, 72%, 38%) were the first results to be obtained. These results do not fit this pattern and have a very large variation, another problem with this result is that ideally the temperature should have been above zero, however this was very hard to achieve using purely ice. This makes me come to the conclusion that the results are inaccurate and the experiment should be retaken. The readings for 60oC (3%, 2%, 2%) were extremely low. If a result was reading 2% the substance would practically be opaque allowing limited amount of light through. However, by visual observation this was not the case, hence it might be a false reading. Having two incorrect results and a discrepancy in the temperature scale, these tests were retaken. I also adjusted the scale by added intermediate temperature points, 30oC and 50oC, to see how this would affect my linear graph. Graph 2 shows results for temperatures 10oC, 20oC, 30oC, 40oC, 50oC and 60oC. The new results for 10oC (84%, 82%, 87%) are much more compliant and have a very small variation, making the average figure 84.3%. This confirms that my previous result was erroneous indeed, possibly due to calibration error and lack of experience. The results for 30oC (70%, 78%, 82%) ...read more.

Conclusion

This concludes that the smaller the intervals between each temperature point the move accurate the results are. Ideally a result should be taken for a temperature point with the interval at 1oC, this will show the exact temperature the proteins denature and pores open to release beetroot pigment. The volume of liquid may have been a source of error. The volume of water in the beaker which is acting as a water bath does not have to be a specific volume. However, it is important that the volume of water within the boiling tube is constant throughout. This was easily achieved by using a small 10cm3 measuring cylinder. This possible error did not affect my results as my accuracy was to 0.1cm3. A nearly 100% accurate measurement can be achieved if a precision pipette is used. Another source of error is the colorimeter. This is a piece of electronic equipment that may malfunction, as possibly happened with the initial result for 10oC. It is vitally important to calibrate the colorimeter before taking a measurement. This did affect my results, once I obtained results for 20oC and saw they were higher in percentage light transmission than for 10oC. The 10oC temperature point was retaken and the results complied. This error is very hard to avoid because it is an electronic piece of apparatus, therefore several results should be taken for every test tube. The number of repeats is an additional source of error. The more repeats done on temperature points the average values calculated will be more reliable. This is the issue with the anomaly at 40oC, if more results were taken for temperature points 40oC and 50oC then it would be clear to see how the averages for these two points truly relate to each other. This did affect my results however, this error was consistent throughout the whole experiment which decreases the errors influence on my results. To overcome this error, more trials should be taken for each temperature point. ?? ?? ?? ?? Alya Gutnikova AS Biology Coursework, 2008 KL/ JJS 1 ...read more.

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3 star(s)

*** This is well written and considered piece of coursework but lacks some of the elements (such as results in a suitably headed table) that are necessary in a piece of A level experimental work.
To improve
Research and rationale
The rationale for the investigation is discussed in terms of its scope and some appropriate biological principles are discussed but there is need for the inclusion of some additional sources of information ( beyond readily available A level textbooks).The selected material could then be used to assist with the planning and the later interpretation of results.
Planning
The aim of the experiment is stated but there is no clearly stated hypothesis. A prediction should be stated and biological knowledge used to explain it. Most of the key variables have been described. The apparatus is listed but needs to be justified. The attempts to assess safety are limited and would need to be more detailed under current guidelines. The method is well written but does lack some key experimental points such as the filter number or wavelength used in the colorimeter.
Observing and recording
Observations have been carried out over a suitable range of values and a sufficient observations have been made to allow a conclusion. This was obvious from the discussion in the conclusion. There are however no results recorded in a suitably headed table which would lose credit in a coursework assessment.
Interpreting and Evaluating
The data was processed but not recorded in the results table. The trends and patterns were identified and results interpreted using some relevant biological principles. The limitations of the procedure were commented on but there were few sensible modifications suggested.

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